1. Technical Field
The present invention relates to a core, and more specifically, to an isolation transformer core applicable to an automobile component and an automotive component including a core comprising an injection molded core member.
2. Related Art
An isolation transformer includes cores having coils thereof arranged to face each other to transmit electric power or an electric signal between each other through electromagnetic coupling of the opposite coils in a contactless manner.
For example, a rotary transformer of this type includes an isolation transformer in which a primary core is fixed and a secondary core is rotatably arranged, and a rotary transformer for a rotary head of a video tape recorder is generally known.
In the rotary transformer, in order to make a coupling coefficient of coils in cores large, cores having a high relative permeability are used and a gap between the cores is restricted to several μm. In the rotary transformer, when the coupling coefficient of the coils is very large, self-inductance and mutual inductance of the two opposite coils cancel each other, so that input-output impedance of the transformer is small. Therefore, in the rotary transformer, impedance matching between the coils and a load can be easily attained.
As cores of the rotary transformer, sintered ferrite cores are generally used. The sintered ferrite core is favorable as a core of a high frequency transformer in that it has a very high relative permeability and produces only a very small eddy-current loss.
In the rotary transformer in which primary and secondary cores are brought into a relative rotation, the size of a gap between the cores has a direct influence on manufacturing cost. In a rotary transformer having a large coupling coefficient of coils, in order to provide a gap between cores of several μm, high manufacturing precision and high assembling precision of components are required, which causes high manufacturing cost. In the case of an automobile, strict restriction is imposed on manufacturing cost and very strong vibration is produced during driving. Therefore, the rotary transformer for an automobile needs to have a gap of 0.5 mm or larger between the opposite cores.
The sintered ferrite core has favorable properties as mentioned above, but has a drawback peculiar to sintered oxide: fragility.
Therefore, when sintered ferrite cores are to be used as cores of a connector for an automobile, for example, cores of a connector for an air bag, various consideration is needed, for example, about how to prevent vibration, how to fix the cores and the like. Also in view of manufacturing cost, the sintered ferrite core is difficult to apply to an automobile component.
An automobile is equipped with, as an automobile component, a rotation sensor for detecting a rotary angle. A rotation sensor of electromagnetic induction type is provided with a first rotor, a stationary core fixed to a stationary member, and a second rotor disposed between the first rotor and the stationary core, for instance. The first rotor and the stationary core are made of a magnetic material having a high permeability. A coil is accommodated in the stationary core. The first rotor and the stationary core form a magnetic circuit. When an excitation current flows through the coil, alternating magnetic field is produced. An automotive rotation sensor is required to be small in size and high in accuracy, and hence a core member (such as the first rotor and a core body of the stationary core) is required to have high flowability during molding.